This invention relates in general to electrical devices including one or more wound coils and more particularly to devices of this type which are provided with an insulating member supported on a laminated winding accommodating structure. The invention is more particularly and concisely described in connection with electric motors.
Many fractional horsepower, relatively low cost, electric motors are conventionally formed with a generally U-shaped laminated yoke section having a rotor receiving bore in the bight portion of the U as described for example in the Myron D. Tupper U.S. Pat. Nos. 3,014,140 and 3,024,377 which issued on Dec. 19, 1961 and Mar. 6, 1962 respectively, and which are assigned to the assignee of this application.
Since the general types of motor construction described in the Tupper patents are now known in the art, further detailed description of the general features and characteristics of such motors will not be specifically set forth herein; and the disclosure of such Tupper patents are specifically incorporated herein by reference.
It is generally recognized that it is necessary to provide means for insulating a motor winding formed of one or more coils from the winding accommodating structure of the motor. Various approaches and techniques used in the past have included the placement of an insulating material around selected portions of the coil accommodating structure and have, at times, included means for positioning the coil turns on the coil accommodating structure. Another approach suggested heretofore in Great Britain Patent 759,960, involves the formation of insulation in situ on, e.g., a salient pole shaded pole stator core. That publication, however, neither recognized problems associated with such an approach nor suggested solutions to such problems.
In the case of the motors shown and described in Kaeding U.S. Pat. No. 3,270,227 (issued Aug. 30, 1966) "integral insulation" may be placed on the winding accommodating structure to provide a ground insulation system. Suitable thermosetting resins may also be used to form a covering for the winding, provide an outer insulation system for the winding, and also firmly and fixedly position the winding on the coil accommodating structure. These approaches, however, do not make it possible to economically provide auxiliary structural members that are formed of insulating material.
In still other approaches, the ground insulation may be formed by insulating tape or by a hardened coating of thermoresponsive material that is applied by brushing or dipping. All of these approaches have turned out to be relatively expensive in actual practice.
In each of the above-mentioned approaches, some means be provided to secure together a stack of laminations at least until the ground insulation has been permanently formed on the lamination stack. Frequently, weld beads or rivets have been used for this purpose. This in turn has contributed to increased manufacturing expense and, in general, has contributed to increased core losses during motor operation.
Still another approach that has been used heretofore (in fractional horsepower sized motors) has included the use of a coil bobbin made of one, two, or more molded parts that are assembled together on an elongated stack of laminations. Wingler et al U.S. Pat. No. 3,189,772 which issued June 15, 1965 illustrates one of these approaches.
The use of preformed insulating bobbins or bobbin parts are often desirable for economic reasons, but this approach too is not completely satisfactory. When lamination stacks are formed from laminations having non-uniform sections, as for example, by having enlarged end sections or enlarged sections intermediate the ends of the laminations (as clearly revealed for example in the aforementioned Tupper U.S. Pat. No. 3,024,377), use of a bobbin with a sleeve having a bore passable over the enlarged sections results in the formation of large air gaps between the lamination stack and bobbin. This, in turn, decreases the heat transfer rate from the winding to the lamination stack and reduces the magnetic flux density induced in the laminations during energization of the winding.
Furthermore, even when generally rectangular shaped laminations are used to form the coil accommodating structure of the motor (as suggested for example in the Wingler et al patent), air gaps between the core and bobbin still occur due to the tolerances that must be provided to assure that a bobbin may be readily assembled on a laminated core. This problem is aggravated by the relatively great variations that occur during manufacture of a laminated core and particularly so in those cases where laminations are bonded together. This approach is also expensive since the bobbins must be preformed, handled, and then assembled on the stack of laminations.
Furthermore, some means should normally still be used to secure the laminations together prior to slipping the bobbin thereon. For example, after a bobbin is slipped onto a stack of laminations, some means such as an adhesive or varnish applied by varnish treatment is used to secure the bobbin to the lamination stack.
Varnish or insulating tape has also often been depended upon to provide protection for the winding. It would, however, be desirable to provide an electric motor wherein the winding portion of the motor is substantially completely surrounded by a moisture resistant molded structure.
Although the above problems have been discussed with particular reference to fractional horsepower motors, it will be appreciated that these problems may also be encountered in the manufacture of other devices. Thus, it will be seen that the resolution of these and other problems would be particularly desirable.